Activity-composition relations in the system CaCO3-MgCO3 predicted from static structure energy calculations and Monte Carlo simulations

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Thermodynamic mixing properties and subsolidus phase relations of the rhombohedral carbonate system, (1 - x) CaCO3 - x MgCO3, were modelled in the temperature range of 623-2023 K with static structure energy calculations based on well-parameterised empirical interatomic potentials. Relaxed static structure energies of a large set of randomly varied structures in a 4 x 4 x 1 supercell of R3c calcite (a = 19.952A , c = 17.061A ) were calculated with the General Utility Lattice Program (GULP). These energies were cluster expanded in a basis set of 12 pair-wise effective interactions. Temperature-dependent enthalpies of mixing were calculated by the Monte Carlo method. Free energies of mixing were obtained by thermodynamic integration of the Monte Carlo results. The calculated phase diagram is in good agreement with experimental phase boundaries.

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Department of Applied Chemistry

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Faculty of Science

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NOTICE: this is the author’s version of a work that was accepted for publication in Geochimica et Cosmochimica Acta. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Geochimica et Cosmochimica Acta, Vol. 71, No. 4 (2006). DOI: 10.1016/j.gca.2006.11.008

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